Mid-Pliocene sea level and continental ice volume based on coupled benthic Mg/Ca palaeotemperatures and oxygen isotopes

Ostracode magnesium/calcium (Mg/Ca)-based bottom-water temperatures were combined with benthic foraminiferal oxygen isotopes in order to quantify the oxygen isotopic composition of seawater, and estimate continental ice volume and sea-level variability during the Mid-Pliocene warm period, ca 3.3-3.0Ma. Results indicate that, following a low stand of approximately 65m below present at marine isotope stage (MIS) M2 (ca 3.3Ma), sea level generally fluctuated by 20-30m above and below a mean value similar to present-day sea level. In addition to the low-stand event at MIS M2, significant low stands occurred at MIS KM2 (-40 m), G22 (-40m) and G16 (-60m). Six high stands of +10m or more above present day were also observed; four events (+10, +25,+15 and +30 m) from MIS M1 to KM3, a high stand of +15m at MIS K1, and a high stand of +25m at MIS G17. These results indicate that continental ice volume varied significantly during the Mid-Pliocene warm period and that at times there were considerable reductions of Antarctic ice.     

Performance-based design in earthquake engineering: a multi-disciplinary review

This paper reviews the contributions of research towards the development of the methodologies associated with Performance-Based Seismic Engineering (PBSE). Research undertaken in various related disciplines is reviewed, under the broad section headings of (i) Engineering Seismology and Geology (Seismic Activity Modelling), (ii) Engineering Seismology (Seismic Hazard Modelling), (iii) Soil Dynamics, (iv) System Dynamics, and (v) Mechanics of Materials (Concrete used as example). The sequence of the discussion is consistent with a typical seismic assessment procedure, which commences with seismic activity modelling in the ‘upstream’ end of the procedure and finishes with consideration of structural mechanics behaviour at the ‘downstream’ end. Each section provides an outline of historical research and development, leading to a review of the state-of-the-art approaches. Particular emphasis is given to the inter-linking of the disciplines, and the paper refers to such links as ‘Nodal Points’. An example of a nodal point is the definition of probabilistic seismic hazard coefficients that are used to define seismic hazard in terms of elastic response spectra, for example the response spectral accelerations at key periods of 0.3 and 1.0 s. Each of the Nodal Points associated with the various disciplines has been critically reviewed, and shortcomings have been identified. For example, the inability of a probabilistic approach to fully represent an earthquake event as a physical process is highlighted. Also, the importance of putting emphasis in future research on determining the Maximum Credible (or Considered) Earthquake, MCE, is emphasised.

The paper brings to light the fact that, although significant achievements have been made in each of the related disciplines and in the connection of the Nodal Points, there has been relatively little change in substance at the Nodal Points themselves. An important outcome of this multi-disciplinary review is the identification of some key limitations in current procedures. The source of these limitations was traced upstream, and thence to the Nodal Points that provide the inter-disciplinary links. This process has been referred to herein as Upstream Feedback. A review of the problems at these links sows the seeds for further development, which would not have been possible had all the recent contributions been confined within the individual disciplines. Such an Upstream Feedback process, enabling improvements to the multi-discipinary links, would be instrumental in enhancing the overall effectiveness of PBSE in the future.     

Quantitative Physiological Assessment of Stress Via Altered Immune Functioning Following Interaction With Differing Automotive Interface Technologies

Technology can enhance or diminish a user's psycho-physiological stress level; the ability to quantify these responses can help evaluate and refine design. The capability of drivers to accomplish basic tasks utilizing differing sensory modalities while maintaining lane discipline within a computer-simulated environment was assessed. Fifteen healthy subjects provided capillary blood samples before and after using three human–machine interface designs—touch-screen, voice control, and multimodal. Using a chemiluminescent technique termed Leukocyte Coping Capacity, the ability of leukocytes to produce reactive oxygen species in vitro was assessed. Significant poststressor changes in leukocyte activity of varying magnitude were observed following the use of all interfaces; with the multimodal interface provoking the most pronounced response and voice control the least. Although still requiring further research, the results support the proposition for using immune responsiveness as a means for quantifying psychological stress during assessment of ergonomic design and psycho-physiological and social interaction.     

The National Ignition Facility neutron time-of-flight system and its initial performance (invited)

The National Ignition Facility (NIF) successfully completed its first inertial confinement fusion (ICF) campaign in 2009. A neutron time-of-flight (nTOF) system was part of the nuclear diagnostics used in this campaign. The nTOF technique has been used for decades on ICF facilities to infer the ion temperature of hot deuterium (D(2)) and deuterium-tritium (DT) plasmas based on the temporal Doppler broadening of the primary neutron peak. Once calibrated for absolute neutron sensitivity, the nTOF detectors can be used to measure the yield with high accuracy. The NIF nTOF system is designed to measure neutron yield and ion temperature over 11 orders of magnitude (from 10(8) to 10(19)), neutron bang time in DT implosions between 10(12) and 10(16), and to infer areal density for DT yields above 10(12). During the 2009 campaign, the three most sensitive neutron time-of-flight detectors were installed and used to measure the primary neutron yield and ion temperature from 25 high-convergence implosions using D(2) fuel. The OMEGA yield calibration of these detectors was successfully transferred to the NIF.     

Case study: an investigation into the cause of `error rate drift'

During product development some Hewlett-Packard DDS tape drives experienced a gradual increase in their uncorrected error rate when running a particular operating test at low humidity. This was known as `error rate drift'. A combination of system-level testing, signal processing, and atomic force microscopy showed that the degradation was caused by contamination on the surface of the heads. The `stain' thickness increased each time tape was reused, resulting in progressive attenuation of the readback signal amplitude. Using time-of-flight secondary ion mass spectroscopy the contaminant was identified as inorganic Fe, Si and Al, transferred from the media.     

In situ strength criteria for tunnel design in highly-stressed rock masses

The selection of rock mass strength parameters and the approach to assessing the mechanical and thermal-mechanical rock mass behaviour around tunnels are important aspects of designing underground openings for a spent nuclear fuel waste repository. This paper demonstrates how strength criteria based on in situ observations can be used to design stable underground openings in rock masses subjected to adverse stress conditions. The findings are based upon work conducted at AECL’s Underground Research Laboratory (URL) regarding rock mass strength around tunnels in sparsely fractured granite.     

Developing tools for excavation design at Canada''s Underground Research Laboratory

A project to develop an excavation design process for potential application in construction of a nuclear fuel waste repository was undertaken in Canada at the Underground Research Laboratory. The excavation design process is seen to have four elements: characterization, modelling, monitoring and design. In moving this project forward, fundamental issues in rock mechanics were addressed. These issues included increasing the understanding of the micro-mechanical phenomena leading to time-dependent cracking in situ; quantifying rock mass damage through field measurements; coupling mechanical rock fracture analyses with thermal and hydraulic numerical tools; using results of laboratory long-term loading tests to calibrate properties related to time-dependent strength degradation, and presenting the results from field measurements, numerical simulations and analytical calculations in terms that are relevant to excavation design. As such, the project encompassed a wide range of geotechnical skills and technologies. The results from the project have important implications for rock mechanics and have applicability beyond the scope of nuclear fuel waste disposal.